Everyday experience creates preconceptions that fail drastically when that experience is extended to the very massive and the very fast, or when extended to the very small and the very cold. The large scale requires relativity theory, and the small scale requires quantum mechanics. Quantum physics deals with "Nature as She is—absurd."

Quantum physics deals with situations where the usual picture of reality breaks down. Photons (discrete units of light) and other very small things have some behaviours that resemble classical particles like billiard balls and other behaviours that resemble classical waves like water waves.

Radiators of photons such as neon lights have spectra, but the spectra are chopped up instead of being continuous. The energies carried by photons form a discontinuous and colour coded series.

The energies, the colours, and the spectral intensities of electromagnetic radiation produced are all interconnected by laws. But the same laws ordain that the more closely one pins down one measure (such as the position of a particle) the more wildly another measure relating to the same thing (such as momentum) must fluctuate. Put another way, measuring position first and then measuring momentum is not the same as measuring momentum first and then measuring position. Even more disconcerting, particles can be created as twins and therefore as entangled entities -- which means that doing something that pins down one characteristic of one particle will determine something about its entangled twin even if it is millions and millions of miles away.

Around the turn of the twentieth century, it became clear that classical physics was unable to explain several phenomena. Understanding these limitations of classical physics led to a revolution in physics: the development of quantum mechanics in the early decades of the last century.